Suo - Mires and peat 66 (2015)

• Ojanen, Luonnonvarakeskus (LUKE) E-mail: paavo.ojanen@helsinki.fi

• Hotanen, Luonnonvarakeskus, Joensuu. PL 68, 80101 Joensuu E-mail: juha-pekka.hotanen@luke.fi
• Saarinen, E-mail: ei.tietoa@nn.oo
• Nousiainen, E-mail: ei.tietoa@nn.oo

Commercial thinning is a common practice when growing even-aged stands in the Nordic countries. Thinning from below is carried out to harvest suppressed and part of the mid-sized trees that cannot successfully compete for resources and have become grown over by co-dominant and dominant trees. In five field experiments, we studied the effects of harvesting method on the nutrient amount of logging residues left at the site in thinning of Scots pine stands. Comparison was carried out between four harvesting methods representing different levels for forest-residue recovery: SOH (stem-only harvesting down to a diameter of 7 cm, SOH-E (stem-only harvesting down to a diameter of 2 cm),WTH (whole-tree harvesting including stems, tops and branches) and WTH-M (WTH and manual collection of those logging residues which were left in mechanical harvesting). In each experiment, logging residues were weighed and sampled for determination of their nutrient concentrations, and soil samples were taken from the surface peat layer (0–20 cm) for nutrient analyses. In SOH treatments, all residues and nutrients bound in the logging residues were left at the site. In WTH 28–67% and in WTH-M 4–20% of the nutrients remained at the site, with the figure depending on the experiment. The amounts of N (1%), P (1–4%), Ca (2–5%), and Mg (3–8%) bound in the logging residues in SOH were low in comparison to the corresponding amounts in the 0–20 cm peat layer. However, the amount of K in logging residues represented 10–26% and the amount of B 8–15% compared with the corresponding nutrients in peat. The amount of N, P, and K in logging residues after CTL harvesting was 39–86, 3–7, and 9–21 kg•ha-1, respectively. The corresponding figures after WTH were 15–36, 1–3, and 3–9 kg ha-1. We assume that WHT on peatland sites that are prone to K deficiency or already have a detected shortage may increase a risk for nutrient imbalances and growth loss in remaining tree stand.

• Hytönen, Natural Resources Institute Finland, Silmäjärventie 2, 69100 Kannus, Finland E-mail: ei.tietoa@nn.oo
• Moilanen, E-mail: ei.tietoa@nn.oo

• Lindholm, E-mail: ei.tietoa@nn.oo